After upgrading to Ubuntu 21.04 seahub again failed to start. The same advise how to fix it with previous version helped:
pip3 install --ignore-installed django-simple-captcha
Afterwards seafile works again. Now need again to fix the office-file previews (which again don’t work).
Seafile has really an issue with standard Ubuntu after 20.x if you are on 7.1.x
Additional things I needed to repeat again to get Office preview and Search working again:
Install again python modules as described in the server manual as requirements to upgrade to 7.1 (pip3 install…)
This solves the office preview and search again (on pro)